With the rapid development of the modern optoelectronic technology, the display technology is developed for being lighter, thinner, more flexible and more transparent. The thin film substrate made of polymer material possesses the characteristics of light weight, flexibility, transparency and excellent comprehensive performance, which can meet the requirements of display technology well.
The most promising polymer material for the flexible substrate should polyimide (PI). Polyimide has excellent heat resistance, radiation resistance, chemical resistance, electrical insulation and mechanical properties. However, the traditional commercial PI film is brown. Mainly it is because the strong spectral absorption of the charge transfer complex (CTC) in or among molecules generated by the electron-withdrawing action of the alternating dianhydride residue and the electron-donating action of the diamine residue in the macromolecule main chain, which significantly restricts the application in transparent flexible display technology. Therefore, for obtaining a colorless transparent polyimide based material, it must be modified to weaken or eliminate the influence of CTC.